Abstract : A method and apparatus for compensating for height variations in certain nuclear gauging applications, particularly nuclear mine detection, are disclosed. A source of monoenergetic photons and a pair of detectors are provided. One of the two detectors includes a K-edge filter, whereas the second detector does not. After processing, the outputs of the two detectors are applied to a suitable readout device. The combination of the filtered detector and unfiltered detector provide a means to compensate for any height variation of the source-detector assembly above the medium under study; thereby permitting any change in the average atomic number of that medium to be discerned. (Author)